This invention relates to active acoustic attenuation systems, and more particularly, to an adaptive multi-channel system.
Active acoustic attenuation involves injecting a canceling acoustic wave to destructively interfere with and cancel an input acoustic wave. Acoustic waves include both sound waves and vibrations. In an active acoustic attenuation system, the output acoustic wave is sensed with an error transducer, such as a microphone, that supplies an error signal to an adaptive filter control model. The adaptive filter control model is normally located in an electronic controller having a central processing unit (i.e. digital signal processor) and input and output parts. The adaptive filter control model supplies a correction signal to a canceling transducer such as a loud speaker. The canceling transducer injects the canceling acoustic wave to destructively interfere with the input acoustic wave so that the output acoustic wave at the error transducer is zero or some other desired value.
In a multi-channel active acoustic attenuation system, multiple input transducers (i.e. sensors) and/or multiple canceling transducers (i.e. actuators) and/or multiple error transducers (i.e. sensors) may be used. Each channel in the adaptive filter control model normally represents a path between one of the input transducers and one of the canceling transducers. It is preferred that the channels in the control model be either intraconnected, or decoupled. Multiple input transducers may be used to provide a plurality of input signals representing the input acoustic wave to the adaptive filter control model. Multiple error transducers may be used to provide a plurality of error input signals representing the output acoustic wave to the adaptive filter control model. The error input signals are used to update each of the channels in the adaptive filter control model. In response to the input signals and/or error signals, the adaptive filter control model supplies a correction signal to each canceling transducer to inject a canceling acoustic wave.
Normally, each input transducer, each canceling transducer, and each error transducer are connected to the adaptive filter control model by a separate, distinct cable. In systems having a small number of transducers, or in systems where the transducers are closely situated to the electronic controller executing the adaptive filter control model, the number of transducer cables does not normally present a problem. However, in systems with numerous transducers; the number, weight, and cost of transducer cables can become a significant concern.
The present invention provides an adaptive multi-channel active acoustic attenuation system for attenuating complex acoustic waves. The system is especially useful for attenuating complex acoustic waves propagating in a duct, a room, a vehicle cab, an airplane, or free space. The system may be used with multiple input sensors and/or multiple canceling actuators and/or multiple error sensors and includes a controller having a communication module and a central processing unit.
One or more input sensor nodes and/or one or more error sensor nodes are also provided in the system. Each node includes a sensor and a network interface. One or more output nodes may also be provided. Each output node includes an actuator and a network interface. A medium physically interconnects each of the network interfaces to the communication module of the controller by means of a control bus or the like. A control network is provided for controlling communication between the communication module of the controller and each of the network interfaces so as to control the flow of data along the medium.